Tuesday, August 26, 2008


Many autopilots incorporate a flight director, a little V-shaped device that pops up on the attitude indicator to tell you where the autopilot thinks it should fly. I've seen the flight director described as the brains and the rest of the autopilot as the muscles of the system. You can engage just the flight director mode of the autopilot, such that you the pilot control all the movements of the airplane, but if you look at the flight director, and set the attitude of the airplane such that the symbolic airplane on the attitude indicator is always aligned with the flight director, then you will fly exactly the way the autopilot would. But without the sick-making trim adjustments.

I first saw a flight director in the cockpit of an airliner. I'm going to guess it was a Canadian Airlines B737, but I'm not sure. The crew turned it on to show it to me, but I remember being unimpressed. It looked like an orange plastic springy toy that came out of a box of Shreddies. And not the fancy new Diamond Shreddies, either.

I don't think very many people use the flight director alone, except perhaps in take-off/go-around mode where they've just disengaged the autopilot, but it's nice to have some direction. I suppose it could be good for training, to take some of the workload off a student. And anything that takes some of the workload off is valuable for any pilot.

It's also valuable if part of the autopilot isn't working properly, but the flight director is. Not just for "oh well I don't have an autopilot today, but at least the flight director works" but for troubleshooting the autopilot. If you engage the autopilot and the airplane dives left while the flight director climbs to the right, that indicates a significantly different problem than if you engage the autopilot and the flight director leads the way into a left spiral dive. In the first case it looks like the trouble is in the control servos while in the other it looks like a problem in the attitude sensing.

There's no flight director on my current ride, so I can't take a picture for you.

And "showing your age" awards to those of you who get the reference in the title of this entry.


Splendor said...

On the B737 we used the FD (two crosshairs in our case) when hand flying part of an instrument procedure: Initial take off, last 500 feet on final or if the autopilot did give in - which happened frequently during drills.
The only time we were allowed to turn them off was during visual approaches.


A said...

I don't know much about Flight Directors, but I do recall that Julie was the cruise director on the Love Boat!

+1, right?

Anonymous said...

I thought it was Otto, with his unfortunately placed inflation valve. Roger?

Colin said...

Julie McCoy, right?

Actress apparently had a terrible cocaine problem and sort of faded from the series.

She was SO cute, though.

Anonymous said...

"I don't think very many people use the flight director alone," ...

On the older gen DC9s we often used the flight director while handflying as we could follow it more smoothly than the Auto pilot did. No one likes to feel a "neg G" bunt-over when intercepting the Glide Slope in cloud! whoopee!

Anonymous said...

My usual autopilot engagement sequence is always:
1) Flight director
2) Modes (HDG, NAV, ALT, ...)
3) Check where the flight director goes
4) Engage the autopilot

So I use it "alone" for a very short time, to avoid any bad surprise when engaging the autopilot.

Anonymous said...

About a quarter century ago, the military cargo plane I was flying (C-141 IIRC) had a flight director only.